1. Field of the Invention
This invention relates to temperature-responsive fluid coupling devices in general, and more particularly to a temperature-responsive fluid coupling device used for a cooling fan of an internal combustion engine.
2. Prior Art of the Invention
There has been introduced a temperature-responsive fluid coupling device which includes a driving shaft driven by an engine, a housing mounted on the shaft in a rotatable state by a suitable bearing, a rotor connected with the shaft, a partition plate dividing an interior of the housing into a reservoir chamber for a viscous shear fluid and a working chamber accommodating the rotor, a fluid return passage formed through the partition plate to return the viscous fluid from the reservoir chamber to the working chamber, a valve plate controlling the fluid communication through the fluid return passage in response to changes in the temperatures of cooling water in an engine radiator, and a pumping passage supplying the viscous fluid from the working chamber to the reservoir chamber, thereby rotating a cooling fan connected to the housing by means of the shear action of the viscous fluid prevailed between the rotor and the housing.
Conventionally, according to a fluid coupling device of this type, if an ignition switch is turned off, the viscous fluid will stand in the bottom of the housing and the fluid will remain in the working chamber. Therefore, if the engine is started again for example in the morning, the cooling fan will be rotated in a state which is almost a direct connection until the viscous fluid has been transferred from the working chamber to the reservoir chamber through the pumping passage, that is to say, an overshoot phenomenon will occur. Consequently, it takes a great deal of time to heat the engine, and also it takes time to heat the interior of a car room.